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Humanizing the yeast origin recognition complex.

ABSTRACT: The Origin Recognition Complex (ORC) is an evolutionarily conserved six-subunit protein complex that binds specific sites at many locations to coordinately replicate the entire eukaryote genome. Though highly conserved in structure, ORC's selectivity for replication origins has diverged tremendously between yeasts and humans to adapt to vastly different life cycles. In this work, we demonstrate that the selectivity determinant of ORC for DNA binding lies in a 19-amino acid insertion helix in the Orc4 subunit, which is present in yeast but absent in human. Removal of this motif from Orc4 transforms the yeast ORC, which selects origins based on base-specific binding at defined locations, into one whose selectivity is dictated by chromatin landscape and afforded with plasticity, as reported for human. Notably, the altered yeast ORC has acquired an affinity for regions near transcriptional start sites (TSSs), which the human ORC also favors.

SUBMITTER: Lee CSK

PROVIDER: S-EPMC7782691 | biostudies-literature | 2021 Jan

REPOSITORIES: biostudies-literature

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Humanizing the yeast origin recognition complex.

Lee Clare S K CSK Cheung Ming Fung MF Li Jinsen J Zhao Yongqian Y Lam Wai Hei WH Ho Vincy V Rohs Remo R Zhai Yuanliang Y Leung Danny D Tye Bik-Kwoon BK

Nature communications 20210104 1

The Origin Recognition Complex (ORC) is an evolutionarily conserved six-subunit protein complex that binds specific sites at many locations to coordinately replicate the entire eukaryote genome. Though highly conserved in structure, ORC's selectivity for replication origins has diverged tremendously between yeasts and humans to adapt to vastly different life cycles. In this work, we demonstrate that the selectivity determinant of ORC for DNA binding lies in a 19-amino acid insertion helix in the ...[more]

PMID: 33397927

Similar Datasets

Humanizing the Yeast Origin Recognition Complex

Project description:The evolutionarily conserved Origin Recognition Complex (ORC), plays a key role in origin selection in eukaryotes. However, ORC is strikingly divergent in its DNA binding specificity, ranging from base-specific interactions in Saccharomyces cerevisiae to base-agnostic interactions in humans. The mechanisms underlying this distinct selectivity is unknown. Atomic model of the yeast ORC showed that base-specific interaction with the invariant thymines of the ARS consensus sequence (ACS) is encoded by a 19-amino acid insertion helix (IH) embedded in the winged helix domain (WHD) of Orc4. This IH is absent in the Orc4 of metazoans including humans, suggesting that removal of the IH might give the yeast ORC “human-like” properties. Indeed, yeast strain engineered with IH deficient Orc4 has completely altered ORC-binding sites enriched in poly-dT tracts located in larger nucleosome-depleted and intergenic open chromatin. In vivo and in vitro assays show that the mutant ORC loads MCM efficiently, in spite of its altered specificity in favor of binding patterns more characteristic of those observed in humans/metazoans. This work provides insights for understanding how ORC evolves to adopt a life cycle that requires plasticity in origin selection during development.

2020-10-18 | GSE149163 | GEO

Humanizing the Yeast Origin Recognition Complex

Project description:Humanizing the Yeast Origin Recognition Complex

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RNA-dependent recruitment of the origin recognition complex.

Project description:The origin recognition complex (ORC) has an important function in determining the initiation sites of DNA replication. In higher eukaryotes, ORC lacks sequence-specific DNA binding, and the mechanisms of ORC recruitment and origin determination are poorly understood. ORC is recruited with high efficiency to the Epstein-Barr virus origin of plasmid replication (OriP) through a complex mechanism involving interactions with the virus-encoded EBNA1 protein. We present evidence that ORC recruitment to OriP and DNA replication function depends on RGG-like motifs, referred to as LR1 and LR2, in the EBNA1 amino-terminal domain. Moreover, we show that LR1 and LR2 recruitment of ORC is RNA dependent. HMGA1a, which can functionally substitute for LR1 and LR2 domain, can also recruit ORC in an RNA-dependent manner. EBNA1 and HMGA1a RGG motifs bound to structured G-rich RNA, as did ORC1 peptides, which interact with EBNA1. RNase A treatment of cellular chromatin released a fraction of the total ORC, suggesting that ORC association with chromatin, and possibly cellular origins, is stabilized by RNA. We propose that structural RNA molecules mediate ORC recruitment at some cellular and viral origins, similar to OriP.

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Crystal structure of the eukaryotic origin recognition complex.

Project description:Initiation of cellular DNA replication is tightly controlled to sustain genomic integrity. In eukaryotes, the heterohexameric origin recognition complex (ORC) is essential for coordinating replication onset. Here we describe the crystal structure of Drosophila ORC at 3.5 Å resolution, showing that the 270 kilodalton initiator core complex comprises a two-layered notched ring in which a collar of winged-helix domains from the Orc1-5 subunits sits atop a layer of AAA+ (ATPases associated with a variety of cellular activities) folds. Although canonical inter-AAA+ domain interactions exist between four of the six ORC subunits, unanticipated features are also evident. These include highly interdigitated domain-swapping interactions between the winged-helix folds and AAA+ modules of neighbouring protomers, and a quasi-spiral arrangement of DNA binding elements that circumnavigate an approximately 20 Å wide channel in the centre of the complex. Comparative analyses indicate that ORC encircles DNA, using its winged-helix domain face to engage the mini-chromosome maintenance 2-7 (MCM2-7) complex during replicative helicase loading; however, an observed out-of-plane rotation of more than 90° for the Orc1 AAA+ domain disrupts interactions with catalytic amino acids in Orc4, narrowing and sealing off entry into the central channel. Prima facie, our data indicate that Drosophila ORC can switch between active and autoinhibited conformations, suggesting a novel means for cell cycle and/or developmental control of ORC functions.

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Developmental regulation of the Tetrahymena thermophila origin recognition complex.

Project description:The Tetrahymena thermophila DNA replication machinery faces unique demands due to the compartmentalization of two functionally distinct nuclei within a single cytoplasm, and complex developmental program. Here we present evidence for programmed changes in ORC and MCM abundance that are not consistent with conventional models for DNA replication. As a starting point, we show that ORC dosage is critical during the vegetative cell cycle and development. A moderate reduction in Orc1p induces genome instability in the diploid micronucleus, aberrant division of the polyploid macronucleus, and failure to generate a robust intra-S phase checkpoint response. In contrast to yeast ORC2 mutants, replication initiation is unaffected; instead, replication forks elongation is perturbed, as Mcm6p levels decline in parallel with Orc1p. Experimentally induced down-regulation of ORC and MCMs also impairs endoreplication and gene amplification, consistent with essential roles during development. Unexpectedly Orc1p and Mcm6p levels fluctuate dramatically in developing wild type conjugants, increasing for early cycles of conventional micronuclear DNA replication and macronuclear anlagen replication (endoreplication phase I, rDNA gene amplification). This increase does not reflect the DNA replication load, as much less DNA is synthesized during this developmental window compared to vegetative S phase. Furthermore, although Orc1p levels transiently increase prior to endoreplication phase II, Orc1p and Mcm6p levels decline when the replication load increases and unconventional DNA replication intermediates are produced. We propose that replication initiation is re-programmed to meet different requirements or challenges during the successive stages of Tetrahymena development.

| S-EPMC4287346 | biostudies-literature

The origin recognition complex: a biochemical and structural view.

Project description:The origin recognition complex (ORC) was first discovered in the baker's yeast in 1992. Identification of ORC opened up a path for subsequent molecular level investigations on how eukaryotic cells initiate and control genome duplication each cell cycle. Twenty years after the first biochemical isolation, ORC is now taking on a three-dimensional shape, although a very blurry shape at the moment, thanks to the recent electron microscopy and image reconstruction efforts. In this chapter, we outline the current biochemical knowledge about ORC from several eukaryotic systems, with emphasis on the most recent structural and biochemical studies. Despite many species-specific properties, an emerging consensus is that ORC is an ATP-dependent machine that recruits other key proteins to form pre-replicative complexes (pre-RCs) at many origins of DNA replication, enabling the subsequent initiation of DNA replication in S phase.

| S-EPMC3779782 | biostudies-literature

Replication licensing regulated by an intrinsically disordered region of origin recognition complex

Project description:In eukaryotes, the hetero-hexameric origin recognition complex (ORC) is responsible for assembling Mcm2-7 complex into a head-to-head double hexamer (DH), forming pre-replicative complex (pre-RC) that licenses origin DNA for replication initiation. This process is tightly controlled throughout the cell cycle to ensure accurate duplication of the genome. Here we show that the N-terminal intrinsically disordered region (IDR) of the yeast Orc2 subunit plays a critical role in promoting pre-RC assembly. We found that removing a short segment (residues 175-200) from Orc2-IDR or mutating a key isoleucine (194) in this region significantly inhibits replication initiation across the genome and causes cell death. Although the Orc2-IDR mutants can still assemble the ORC-Cdc6-Cdt1-Mcm2-7 (OCCM) intermediate on DNA, the assembled mutant OCCM exhibits impaired ATP hydrolysis, preventing its conversion into Mcm2-7-ORC (MO) complex and subsequent DH formation. Interestingly, our in vitro assays showed that adding the Orc2-IDR peptide in the pre-RC reactions can rescue this defect. Furthermore, phosphorylation of this Orc2-IDR motif by S-cyclin dependent kinase (S-CDK) blocks its binding to Mcm2, leading to defective pre-RC assembly. Our findings provide crucial mechanistic insights into the multifaceted roles of ORC in modulating MCM loading to support origin licensing during the G1 phase and its regulation to restrict origin firing within the S phase.

2024-09-18 | GSE262693 | GEO

Assembly of functionally active Drosophila origin recognition complex from recombinant proteins.

Project description:In eukaryotes the sites for the initiation of chromosomal DNA replication are believed to be determined in part by the binding of a heteromeric origin recognition complex (ORC) to DNA. We have cloned the genes encoding the subunits of the Drosophila ORC. Each of the genes is unique and can be mapped to discrete chromosomal locations implying that the pattern and developmental regulation of origin usage in Drosophila is not regulated solely by a large family of different ORC proteins. The six-subunit ORC can be reconstituted with recombinant proteins into a complex that restores DNA replication in ORC-depleted Drosophila or Xenopus egg extracts.

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Identification and reconstitution of the origin recognition complex from Schizosaccharomyces pombe.

Project description:The origin recognition complex (ORC), first identified in Saccharomyces cerevisiae (sc), is a six-subunit protein complex that binds to DNA origins. Here, we report the identification and cloning of cDNAs encoding the six subunits of the ORC of Schizosaccharomyces pombe (sp). Sequence analyses revealed that spOrc1, 2, and 5 subunits are highly conserved compared with their counterparts from S. cerevisiae, Xenopus, Drosophila, and human. In contrast, both spOrc3 and spOrc6 subunits are poorly conserved. As reported by Chuang and Kelly [(1999) Proc. Natl. Acad. Sci. USA 96, 2656-2661], the C-terminal region of spOrc4 is also conserved whereas the N terminus uniquely contains repeats of a sequence that binds strongly to AT-rich DNA regions. Consistent with this, extraction of S. pombe chromatin with 1 M NaCl, or after DNase I treatment, yielded the six-subunit ORC, whereas extraction with 0.3 M resulted in five-subunit ORC lacking spOrc4p. The spORC can be reconstituted in vitro with all six recombinant subunits expressed in the rabbit reticulocyte system. The association of spOrc4p with the other subunits required the removal of DNA from reaction mixture by DNase I. This suggests that a strong interaction between spOrc4p and DNA can prevent the isolation of the six-subunit ORC. The unique DNA-binding properties of the spORC may contribute to our understanding of the sequence-specific recognition required for the initiation of DNA replication in S. pombe.

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CDC45, a novel yeast gene that functions with the origin recognition complex and Mcm proteins in initiation of DNA replication.

Project description:The CDC45 gene of Saccharomyces cerevisiae was isolated by complementation of the cold-sensitive cdc45-1 mutant and shown to be essential for cell viability. Although CDC45 genetically interacts with a group of MCM genes (CDC46, CDC47, and CDC54), the predicted sequence of its protein product reveals no significant sequence similarity to any known Mcm family member. Further genetic characterization of the cdc45-1 mutant demonstrated that it is synthetically lethal with orc2-1, mcm2-1, and mcm3-1. These results not only reveal a functional connection between the origin recognition complex (ORC) and Cdc45p but also extend the CDC45-MCM genetic interaction to all known MCM family members that were shown to be involved in replication initiation. Initiation of DNA replication in cdc45-1 cells was defective, causing a delayed entry into S phase at the nonpermissive temperature, as well as a high plasmid loss rate which could be suppressed by tandem copies of replication origins. Furthermore, two-dimensional gels directly showed that chromosomal origins fired less frequently in cdc45-1 cells at the nonpermissive temperature. These findings suggest that Cdc45p, ORC, and Mcm proteins act in concert for replication initiation throughout the genome.

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